Sonerai II L larger rudder

[BJC]

I wonder why Paz does that

Because the aircraft yaws / pitches / rolls about the CG.


BJC

 

[mcrae0104]

Because the aircraft yaws / pitches / rolls about the CG.

Yes, understood. I'm curious why Paz uses CG to 1/4 tail chord to define the tail arm, whereas all others seem to define it as 1/4 wing chord to 1/4 tail chord.

 

[Vigilant1]

Yes, understood. I'm curious why Paz uses CG to 1/4 tail chord to define the tail arm, whereas others define it as 1/4 wing chord to 1/4 tail chord.

A guess: Pazmany is just being a bit more conservative (by basing calcs on the shortest allowable tail arm)? The CG window is typically about 25% MAC to 40% MAC. If the CG is allowed to be at 40% MAC, the plane will pivot there and it is the appropriate location for defining one end of the tail arm.
My question would be the complement of yours: Why do others calculate tail arm measured from 25% MAC?

 

[mcrae0104]

Why do others calculate tail arm measured from 25% MAC?

I don't know. Using the CG makes more sense to me, but I'm guessing maybe it doesn't matter much in most cases. At any rate, the tail volume coefficients are just a first-pass tool to get in the ballpark for stability.

 

[Pops]

On the JMR I used 25% and with me and full fuel my flying CG is 25.5 %.

 

[addaon]

I wonder why Paz does that.

Moments act around the CG.

 

[mcrae0104]

Moments act around the CG.

Please see post 22. This is a question about why different sources use different definitions of tail length.

 

[addaon]

This is a question about why different sources use different definitions of tail length.

If you want to analyze from first principals, you're going to want to use CG as the basis, since otherwise the comparison is invalid. If you want to compile a database of best practices to build an empirical model from, you're going to want to use quarter chord, since you can extract that from only a three view.

 

[Elviar]

The first Sonerai was designed for racing, so everything except horsepower was minimized, including the rudder. Many builders have added three or four inches the the rudder height, and many different shapes have been used. I added three inches of height to my rudder on my Sonerai IIL, and copied the profile of the P-40 just because I like it. It hasn't flown yet, so I can't comment on performance.